In previous work in this laboratory, we have demonstrated that the availability of iron and the microbial ability to acquire iron are critical events in the pathogenesis of experimental infections with Neisseria gonorrhoeae and other Gram-negative pathogens and potential pathogens. Iron is an essential nutrient for all life forms including bacteria, and components of the host defensive mechanisms depend on the degree of iron-saturation of iron-binding host proteins, like transferrin and lactoferrin. With respect to the gonococcus: (a) avirulent colony types can be made more virulent by supplementation of the inoculum with iron; (b) virulent colony types of urogenital isolates can be made less virulent by "desaturating" the host's serum iron-binding capability; (c) strains isolated from disseminated infections in man retain their virulence even when iron saturation is reduced; (d) a disseminating prototrophic strain produced a siderophore, detectable in unconcentrated culture filtrate, which stimulated gonococcal growth in iron-limited media; (e) but culture filtrates of urogenital isolates require extraction and concentration before siderophore activity can be detected; and (f) unlike siderophores of other Gram-negative bacteria, the gonococcal siderophore appears to be specific for gonococci. Therefore the primary objectives of the proposed research are to isolate and characterize the gonococcal siderophore; to define further its role in pathogenesis of infections caused by N. gonorrhoeae; to determine its role in serum sensitivity or resistance of N. gonorrhoeae, and in resistance and sensitivity to phagocytosis and intracellular killing; and to attempt to identify the outer membrane protein which is responsible for recognition of the siderophore and iron transport in gonococci. The siderophore will be produced and extracted from a diphasic iron-deficient medium, which we have developed, which stimulates (or derepresses) gonococcal siderophore production. Effects of the siderophore on virulence will be evaluated experimentally in the chick embryo model. The availability of iron and the microbial ability to acquire iron may explain a variety of perplexing clinical observations on infections with N. gonorrhoeae.